man man; cat books |grep $key_concepts |grep -v garbage > /dev/null

1. Check disk space usage
2. List all processes currently running
3. Compress and decompress a file
4. Properly shutdown the system
5. Check free space left on a file system
6. Remove user accounts
7. Change the owner or group of a file
8. Change a user’s forgotten password
9. Change access to a directory
10. Run a process on the background